Acoustic and temporal birdsong measurements

In tropical birds, survival is dependent on the ability to effectively communicate with others against a background of high ambient noise. The Acoustic Niche Hypothesis proposes that the deterrent selective force of signal masking has caused animals sharing a habitat to partition their calling behaviour amongst the acoustic bandwidths available, so as to minimise interference between one another. Whether and why species share the so-called ‘acoustic space’ remains a gap in our understanding of animal ecosystems. The aim of this study was to investigate differences between the acoustic structure of avian communities in two spatially distinct habitats in the montane tropical forests of the Caparaó National Park in south-eastern Brazil, and to test whether the distribution of birdsong at each conformed to the ANH. Birdsong from nine hours of passive acoustic recordings at each study site were analysed using principal component analyses. The results contradicted the ANH, revealing strikingly similar patterns of synchronised vocal behaviour. No correlation was evident between the acoustic and temporal partitioning behaviour of songbirds. This study provides a novel comparative analysis of the acoustic dynamics in two separate and diverse avian communities and support for theories of synchronized vocal behaviour in such groups.